An aircraft may include one or more engines mounted to the wings, empennage or other structure of the aircraft. To improve aerodynamics of the flow of air around and/or into the engine, engines are typically housed in a nacelle, which includes a lip skin at the inlet of the nacelle.
The lip skin is typically an aerodynamically shaped annular member. The lip skin is usually formed of aluminum, but may be formed of other impact resistant materials, such as titanium. The lip skin includes a curved leading nose, an outer trailing surface, the outer trailing surface extending from the nose and terminating in an edge, and an inner trailing surface, the inner trailing surface extending from the nose and terminating in an edge. The lip skin may thus define a pocket formed by the nose, the outer trailing surface and the inner trailing surface. The lip skin, which may be relatively thin along its length, may lack rigidity. Additional structural components may be mounted in the lip skin to improve the lip skin's performance in bending and torsion. It may be desirable for the lip skin to be smooth and devoid of irregularities and discontinuities so as to reduce drag and to avoid the creation of turbulence and great effort is typically required to design and implement such a lip skin.
Lip skins typically have complex shapes that can be difficult to manufacture. Lip skins are typically produced by multiple-stage deep draw operations, bulge forming, or spin forming, requiring complex and costly tooling and time consuming multi-step processing. A lip skin may have compound curved profiles or be contoured, e.g., as may be dictated based on desired aerodynamic performance. For example, a lip skin may be contoured or curved along a length of the lip skin (e.g., along the forward-aft direction) as well as circumferentially. As a result, it can be difficult to meet tolerance and/or waviness requirements for joining the lip skin to an associated bulkhead. The lip skin may be joined to other structure, for example a bulkhead arranged internally in the pocket defined by the lip skin. In conventional lip skins, waviness in the contoured surface may be introduced at the joints, for example due to skin pull-up/deflection at the locations where the skin is joined to other structure. Conventional lip skin designs are typically sensitive to longitudinal placement (e.g., along the forward-aft direction) of the mating parts. Waviness or disturbances along the lip skin or imperfect assembly of such more sensitive designs may cause the airflow along the lip skin to become turbulent which may increase the drag and consequently the energy consumption of the aircraft. Precise manufacturing and assembly tolerances may be required, which typically drives complexity and costs up, and drives rates of production down.
Accordingly, it may be desirable to provide a joint, for example for a lip skin of a nacelle, which may be suitable for laminar flow.